Snowmobiles conventionally have a lubrication system that uses an oil pump that is mechanically driven by an engine of the snowmobile. This type of oil pump is generally referred to as a mechanical oil pump.
When the engine operates on a four-stroke principle, the lubricant is stored in an oil tank that is usually connected or integrated to the engine, such as an oil pan. The mechanical oil pump pumps the lubricant from the oil tank to make it circulate through the engine. After circulating through the engine, the lubricant is returned to the oil tank.
When the engine operates on a two-stroke principle, the lubricant is stored in an oil tank that is usually spaced apart from the engine. The mechanical oil pump pumps the lubricant from the oil tank to the crankcase of the engine. From the crankcase, the lubricant flows to the cylinders where it is combusted with a mixture of fuel and air. Since the lubricant is combusted by the engine, the oil tank occasionally needs to be refilled with lubricant for the engine to operate properly.
By having the mechanical oil pump driven by the engine, the amount of lubricant being pumped is directly proportional to the speed of the engine. Therefore, the faster the engine turns, the more lubricant is being pumped by the mechanical oil pump, and the relationship between engine speed and the amount of lubricant being pumped is a linear one. However, the actual lubricant requirements of an engine, especially in the case of an engine operating on a two-stroke principle, are not linearly proportional to the engine speed.
Some mechanical oil pumps driven by the engine are also linked to the throttle lever that is operated by the driver of the vehicle, such that the position of the throttle lever adjusts the output of the mechanical oil pump. Although this provides for an improved supply of lubricant to the engine, it does not account for other factors which affect the actual lubricant requirements of the engine such as ambient air temperature and altitude.
For a two-stroke engine, the actual lubricant requirement depends, at least in part, on the power output of the engine, not engine speed. The higher the power output, the more lubricant is required. There are instances during the operation of the two-stroke engine where the engine speed is high, but where the power output of the engine is low. In such instances, the mechanical oil pump driven by the engine provides a lot of lubricant even though the actual requirements are low. One such instance is when the track of the snowmobile is slipping on a patch of ice. In this instance the engine speed is high due to the slippage, but the actual power output is low. There are other instances where the actual lubricant requirements are lower than what would be provided by a mechanical oil pump driven by the engine. For example, at start-up, all of the lubricant that was present in the engine when it was stopped has accumulated at the bottom of the crankcase. The accumulated lubricant would sufficient to lubricate the engine for the first few minutes of operation, however the mechanical oil pump, due to its connection to the engine, adds lubricant regardless. Therefore, in the case of an engine operating on the two-stoke principle, using a mechanical oil pump results in more lubricant being consumed by the engine than is actually required. This also results in a level of exhaust emissions that is higher than a level of exhaust emissions that would result from supplying the engine with its actual lubricant requirements since more lubricant gets combusted than is necessary.
The actual lubricant requirements of an engine for a snowmobile are also a function of one or more of the altitude at which the snowmobile is operating, the engine temperature, and the position of the throttle lever, to name a few. Since snowmobiles are often operated in mountainous regions and that temperatures can vary greatly during the winter, the actual lubricant requirements of the engine can be significantly affected by these factors and therefore need to be taken into account. Conventional snowmobile lubrication systems using mechanical oil pumps, due to the linear relationship between the engine speed and the amount of lubricant being pumped, cannot take these into account.
In the prior art, mechanisms were provided on some snowmobiles which would modify the amount of lubricant provided by the oil pump per engine rotation. These mechanisms provided two (normal/high, or normal/low) or three (normal/high/low) oil pump settings. Although these settings provided some adjustment in the amount of lubricant being provided to the engine by the oil pump, since the pump is still mechanically connected to the engine, the relationship is still a linear one, and thus does not address all of the inconveniences described above. The settings simply provide consistently more or less lubricant, as the case may be, than at the normal settings.
Therefore, there is a need for a snowmobile having a lubrication system that provides an engine of the snowmobile with an amount of lubricant that is at or near the actual lubricant requirements of the engine.
There is also a need for a snowmobile having a lubrication system that supplies lubricant to an engine of the snowmobile non-linearly with respect to the engine speed and other factors.
Also, since a mechanical oil pump in snowmobiles is driven by the engine, the power required by the engine to drive the pump cannot be used to drive the track of the snowmobile.
Therefore, there is a need for a snowmobile having a lubrication system that requires less power from the engine than would be necessary to drive a conventional mechanical oil pump.
Finally, since snowmobiles are used during the winter, the ambient temperature can occasionally be low enough that the lubricant becomes too viscous to be efficiently pumped.
Therefore, there is also a need for a snowmobile having a lubrication system that can pump lubricant at low temperatures and for a method of operating the lubrication system.